I do believe that Depression is always physiological. There is great value, though, in being able to fully feel the Depression and stay in control, to separate it from "yourself". Over time these negative feelings have less and less affect on you. This concept is why some people are able to control their anger while others are very reactive.
It is very challenging at times but building up this pain/discomfort tolerance is a huge part of my recovery strategy.
But like I said it seems like you have an informed, logical approach to medications and drugs and would be more than willing to get off them if it was prudent.